1. Technical Field of the Invention
The present invention relates to an apparatus that controls the acceleration of a vehicle at a target value of the acceleration.
2. Related Art
In the field of control of vehicle speeds, various types of control techniques have been known. Such techniques include a technique to automatically control the speed of a vehicle at a desired value based on distances between two vehicles, which is called ACC (adaptive cruise control) and a technique to reduce the speed of a vehicle down to an appropriate value for cornering a curve before entering the curve. These control techniques are disclosed by Japanese Patent Laid-open Publication Nos. 2000-108721 and 2008-30677, respectively.
Another control technique was presented in Fraunhofer ISST workshop COMPARC (Berlin, May 29, 2008). This technique provides, as two individual functional controllers, not only a speed controller which decides a target acceleration for realizing a target speed by deciding it using information indicative of the running state of a preceding vehicle but also an acceleration controller which decides a drive force for realizing the decided target acceleration. According to this technique, it is possible to provide the speed controllers which work irrespective of the characteristics of actuators mounted in vehicles, so that it may be effective for developing an acceleration control apparatus as a whole.
Another acceleration controller, which is similar in configuration to the above workshop-shown acceleration controller, is also shown by Japanese Patent Laid-open Publication No. JP 2006-506270 A, This acceleration controller controls smoothly a vehicle acceleration at a target acceleration value calculated by a speed controller. To realize this smooth control of the acceleration, the acceleration controller is also provided with means to limit a jerk, which is an amount of changes in the acceleration which is an unpleasant motion, so that a sudden change in the acceleration can be avoided. This jerk limiting means is useful in smoothly controlling the vehicle acceleration as long as the acceleration controller controls the acceleration at appropriately designed control intervals, even when the control intervals (i.e., calculation intervals) for the target acceleration are delayed for some reasons in the speed controller.
However, it is pointed out that, in some running states of a vehicle, the delay in the acceleration control, which is due to the jerk limitation control, becomes larger. This results in giving drivers an unpleasant feeling.